1. Field of the Invention
The present invention relates to a toggle type mold clamping device used for an injection molding machine and the like.
2. Description of the Related Art
In an injection molding machine, a mold clamping device and an injection machine are installed in a line on a machine base in general. FIG. 7 is a top view showing an essential portion of a prior art mold clamping device Mc disclosed in Japanese Patent Application Laid-Open No. 9-57805 and having link units 17 and FIG. 8 is a sectional view of the essential portion. FIG. 8 is a partially transparent view showing a locked-up state of the mold clamping device Mc on an upper side of a center line CL of the mold clamping device and a maximum mold opening stroke of the mold clamping device Mc on a lower side of the center line CL.
The mold clamping device Mc includes a fixed platen 1, a movable platen 2, and a rear platen 3 in order to open and close a mold. The fixed platen 1 and the rear platen 3 are coupled by a plurality of tie bars 4 and the movable platen 2 moves forward and backward with respect to the fixed platen 1 along the tie bars 4. The movable platen 2 is moved forward and backward by the link units 17 of a mold clamping mechanism driven by a driving motor (not shown).
The link unit 17 includes a first link 11, a second link 12, and a toggle driving link 13. A through hole into which a bushing is inserted is formed in each of opposite ends (one end and the other end) of the first link 11. Furthermore, another through hole is formed at an intermediate position between the through holes in the opposite ends of the first link 11.
A link pin 15B is inserted through through holes formed in protruding portions 3a of the rear platen 3 and is fixed to the protruding portions 3a of the rear platen 3 by a locking screw or the like. The link pin 15B fixed to the protruding portions 3a of the rear platen 3 passes through the bushing inserted into the through hole 16 formed in the one end of the first link 11. As a result, the first link 11 is enabled by the bushing, inserted into the through hole 16 formed in the one end of the first link 11, to rotate about a central axis of the link pin 15B, passing through the bushing, with respect to the protruding portions 3a of the rear platen 3.
A link pin 15A is inserted through the through hole formed in the other end of the first link 11 and is fixed to the other end of the first link 11 by a locking screw or the like. A through hole 16 into which the bushing is inserted is formed in one end of the second link 12. The link pin 15A inserted through the through hole formed in the other end of the first link 11 passes through the bushing inserted into the through hole 16 formed in the one end of the second link 12. As a result, the first link 11 and the second link 12 are enabled by the bushing, inserted into the through holes formed in the other end of the first link 11 and the one end of the second link 12, to rotate with respect to each other about a central axis of the link pin 15A passing through the bushing.
A through hole 16 into which a bushing is inserted is formed in the other end of the second link 12. A link pin 15C is inserted through through holes formed in protruding portions 2a of the movable platen 2 and is fixed to the protruding portions 2a of the movable platen 2 by a locking screw or the like. As a result, the second link 12 is enabled by the bushing, inserted into the through hole 16 formed in the other end of the second link 12, to rotate about a central axis of the link pin 15C, passing through the bushing, with respect to the protruding portions 2a of the movable platen 2.
A through hole 16 into which the bushing is inserted is formed at each of opposite ends of the toggle driving link 13. A link pin 15D is inserted through the bushing inserted into the through hole 16 formed in the one end of the toggle driving link 13. The link pin 15D inserted through the bushing is fixed to one end of a crosshead 14 by a locking screw or the like. By inserting the bushing into the through hole 16 formed in the one end of the toggle driving link 13, the toggle driving link 13 can rotate about the bushing with respect to the crosshead 14. A link pin 15G is inserted through the bushing inserted into the through hole 16 formed in the other end of the toggle driving link 13. The link pin 15G inserted through the bushing is fixed to the intermediate portion of the first link 11 by a locking screw or the like. By inserting the bushing into the through hole 16 formed in the other end of the toggle driving link 13, the toggle driving link 13 and the first link 11 can rotate with respect to each other about a central axis of the link pin 15G passing through the bushing.
Here, portions rotating with respect to each other about the link pin 15A, the link pin 15B, the link pin 15C, the link pin 15D, and the link pin 15G as central axes are referred to as a pivot portion A, a pivot portion B, a pivot portion C, a pivot portion D, and a pivot portion G, respectively. By providing the pivot portion G on an outer side of the first link 11 as viewed from the crosshead 14 and pivotably coupling the toggle driving link 13, it is possible to extend a span of the toggle driving link 13 without considerably displacing the link unit 17 outward away from the crosshead 14 to thereby increase a mold clamping force and prevent increase in a vertical width of the mold clamping device Mc. By providing the pivot portion G of the first link 11 and the toggle driving link 13 on the outer side, it is possible to shorten a moving distance of the crosshead 14 required to move the movable platen 2 a certain distance to shorten a time for a cycle required to carry out injection molding.
In the mold clamping device Mc described with reference to FIGS. 7 and 8, as shown on the upper side of the center line CL in a one-dot chain line shown in FIG. 8, the link pin 15G receives a load toward the outside of the mold clamping device Mc from the toggle driving link 13 at the pivot portion G of the first link 11 and the toggle driving link 13 in clamping the mold and therefore bending forces are applied on the link pin 15A and the link pin 15G. The first link 11 is divided into two in order to secure an interval through which the toggle driving links 13 passes (as shown with reference numerals 11a and 11b shown in FIG. 9) in carrying out mold closing, mold clamping, and mold opening. The first link 11 is inclined so that its center bulges as shown in FIG. 9 and therefore does not suppress bending of the link pin 15G. At this time, slips occur in a fixed portion of the link pin 15G (a portion in contact with the through hole formed in the central portion between the opposite ends of the first link 11) and a fixed portion of the link pin 15A fixed to the first link 11 and therefore the casts are likely to wear at the fixed portions.
Furthermore, if the link pin 15A of the pivot portion A is inserted into the through hole 16 formed in the second link 12 in order to increase rigidity of the toggle, the toggle pin 15A restricts a movable range of the toggle driving link 13. In some cases, it is necessary to additionally form a back clearance in the toggle driving link 13 as shown in FIG. 10, which reduces strength of the toggle driving link 13.